1. Field of the Invention
The invention pertains to adjustable seat suspensions, particularly for vehicles, wherein the seat is mounted upon a scissors linkage, and the supporting biasing force for the seat is adjustable over a wide range.
2. Description of the Related Art
Off road equipment such as lift trucks, backhoes, Bobcats, and the like, often utilize a spring supported seat to cushion the driver during vehicle operation. Such cushioning usually utilizes extension or compression springs which support the driver's weight. However, because of variations in the driver's weight, often in excess of 100 pounds, it is difficult to "tune" a spring supported seat suspension to provide optimum comfort. Accordingly, it is known to employ seat suspensions utilizing extension or compression springs wherein the biasing force imposed by the springs on the seat structure is adjustable.
In my U.S. Pat. No. 5,601,338, I disclose a vehicle seat structure with an adjustable suspension of the extension spring type. In this patent, the seat is pivoted at its forward edge, and the rear edge is supported by a pair of extension springs. An adjustably positionable slide located upon a lever arm is interposed between the springs and the seat rear portion wherein adjustment of the slide upon the lever means varies the extent of spring biasing force by changing the location of the application of the biasing force to the lever, and in this manner, the seat disclosed in U.S. Pat. No. 5,601,338 may be adjusted to provide an operative suspension for a wide weight range of vehicle operators.
In U.S. Pat. No. 5,601,338, only the seat bottom is capable of suspension, but in some applications wherein large shocks or impacts are transmitted to the seat structure through the vehicle, it is desirable to have greater support and impact absorption than is possible with the prior art devices.
Further, to achieve maximum comfort in a spring supported seat having a back, it is highly desirable that both the back and seat portions move in unison during suspension, and in the prior art, a full seat adjustable suspension device capable of utilization with a wide range of weights of users has not been readily available.